Collaborative Research: Growth of oceanic lower crust: an integrated high-precision geochronologic and trace-element approach

尽管海洋岩石圈覆盖了地球表面的60%以上，但由于缺乏对海底喷发的火山岩下面的侵入岩的地质年代学限制，海洋岩石圈在大洋中脊形成的模型一直受到阻碍。锆石是辉长岩和洋壳中其他侵入岩中发现的难熔矿物，在U-Pb测年方面取得的最新进展，现在可以测量侵入岩的年龄。本研究使用二次离子质谱仪(SIMS)和热电离质谱(TIMS)相结合的方法来追求这一目标。来自西南印度洋海脊735B孔的侵入辉长岩样本将被分析。SIMS是一种高分辨率但不确定性大的技术，可以在微米尺度上测量地球化学差异，将被用于确定锆石中分带的微量元素组成。高精度的锆石同位素稀释TIMS测年将被用来确定样品的岩浆演化。所测年龄的不确定度预计为12000年或更短。这种精确度将提供前所未有的洞察力，了解洋壳在缓慢扩张的海脊生长需要多长时间。这项工作的更广泛影响包括博士后培训和指导。它还促进机构间合作，并将支持来自EPSCoR国家的两个个人投资项目，其中一个来自科学界代表性不足的性别。将向剑桥马萨诸塞州地区的高中开展外联活动，并将为它们制作有关地质年代学的教材。该项目的结果将被存档在NSF资助的公众可访问的数据库中。

Although oceanic lithosphere covers more than 60% of the earth's surface, models for its formation at mid-ocean ridges have been hampered by a lack of geochronological constraints on intrusive rocks that underlie volcanic rocks erupted on the seafloor. Recent advances in the U-Pb dating of zircons, refractory minerals that are found in gabbors and other intrusive rocks in ocean crust, now allow dates of intrusions to be measured. This research pursues this objective using a combined secondary ion mass spectrometry (SIMS) and thermal ionization mass spectrometry (TIMS) approach. Samples of intrusive gabbros from Hole 735B on the Southwest Indian Ridge from the Ocean Drilling Program will be analyzed. SIMS, which is a high resolution but large uncertainty technique that can measure geochemical differences on a micron scale, will be used to determine the trace element composition of zoning in zircons. High precision isotope dilution TIMS dating of the zircons will be used to determine the magmatic evolution of the samples. Uncertainties in the ages measured are expected to be 12,000 years or less. This precision will provide unprecedented insight into how long it takes for ocean crust to grow at slow spreading ridges. Broader impacts of the work include postdoctoral training and mentoring. It also fosters inter-institutional collaboration and will support two PIs, one of whom is from a gender under-represented in the sciences, from an EPSCoR state. Outreach to high schools in the Cambridge MA area will be carried out and educational materials for them will be created on geochronology. Results of the project will be archived in NSF-funded publicly accessible databases.